The invention relates to a releasing device for pyrotechnic elements, such as firing elements, gas generators, belt tighteners, electronic detonators, etc., in accordance with the preamble of the first claim.
With electronic pyrotechnic systems, in particular with those that are used in the automotive field and as electronic detonators, all the functions, such as overvoltage protection, limiter structures, filtering properties, address allocations, arming codes and setting of the delay times are achieved with the aid of a circuit comprising electronic components. The centrepiece is an integrated circuit in a chip. Due to the small structure, for example of a detonator, the chip is mounted in a space-saving manner on a printed circuit board (PCB) using the so-called CoB (chip on board) technology. The functional reliability of the circuit and its security with respect to faults are the most important quality criteria.
This CoB technology has, however, disadvantages that may result in reliability problem. Because of the relatively sensitive bonding points, damage may occur in the production process as a result of the mechanical stress loads encountered during soldering, welding, punching, joining or shrinking. In the extreme case, these may result in contact open-circuits or unstable contacts.
For this reason, it is already known to accommodate the integrated circuits (crystals) in an IC housing (for example, SOT). An electronic igniter having a chip in such a housing is disclosed, for example, in EP 0 616 190 A1.
An object of the present invention is to make releasing units for pyrotechnic systems still more defect-safe and failure-safe by configuring the electronic circuit and providing test possibilities.
The object is achieved according to the present invention, which relates to an electronic releasing device for pyrotechnic igniters having a primary and a secondary charge. The primary charge is ignited by means of a circuit that comprises electronic components and whose essential electronic components are accommodated as an integrated components as an integrated circuit in an IC housing, with the housing being disposed on a printed circuit board. The terminals of the IC housing are provided as connecting points for test instruments for checking the serviceability of the integrated circuit and the igniter function and also serve for connection to external electronic devices for programming the releasing device with the aid of the characterizing features of the first claim. Advantageous embodiments of the invention are claimed in the subclaims.
With conventional CoB technology, the integrated circuit is designed only for previously specified functions. After the chip has been mounted on the printed circuit board, its terminals are inaccessible as a result of coating with a covering composition. As a result, its functions can no longer be tested. Individual inputs into the integrated circuit are no longer possible. The encapsulation of an integrated circuit in a housing has the advantage that each of its terminals, in particular the test points, are brought out and are thereby accessible. At these terminals, contact points may be provided for testing instruments that enable speeding up of checking of the serviceability of the integrated circuit. The new technology makes it possible to provide a chip that, after its installation, can be loaded via the contact points with the appropriate functions provided for use, in particular the fuse address allocations, the arming code and the setting of the delay times. As a result, individual programming of any igniter is possible with respect to its application purpose.
In addition, a chip encapsulated in an IC housing offers the possibility for the performance data of the integrated circuit to be capable of being tested at the manufacturer""s premises and before installation in the releasing unit, even under climatic conditions. In particular, with guarantee demands imposed on the manufacturer of the IC, the verification duty with faults that occur under cold conditions are very problematical since the crystal surfaces become iced up and an error determination is prevented. In temperature chambers, the serviceability of the integrated circuit can be tested both at low and at high temperatures, and with predetermined atmospheric simulations, such as humidity and dryness. Because of the accessible terminals, that is possible for every integrated circuit prior to installation. As a result, the failure rate that had to be accepted with the installation of previously untested integrated circuits using CoB technology is drastically reduced.
In a further embodiment of the invention, the chassis grounds of the integrated circuit are brought out at more than one connection point. This ensures that a large-area and defined chassis potential is always applied even with defective chassis bonds. Floating chassis potential causes faults. The multiple contacting of the chassis therefore advantageously achieves high immunity, in particular towards high-frequency electromagnetic radiation.
Depending on the nature of the integrated circuit, the fuse addresses and/or functional priorities can be stored in a memory (for example, EEPROM) in the integrated circuit. That is advantageous if the releasing unit is programmed only shortly before it is used.
If the releasing unit is to be provided only for a certain use for which a fixed programming is provided, for example for a certain fuse address, it may be advantageous if a preset releasing unit is provided separately for every fuse address. In this case, the respective fuse address may be disposed in the form of an already predetermined conductor track pattern on the printed circuit board. This avoids the conventional, expensive cutting of certain conductor tracks (coding) on a so-called programming field on a printed circuit board manufactured in common for all the ignition time steps. The mechanical or thermal cutting of certain conductor tracks, hitherto necessary, to produce certain fuse addresses can result in malfunctions as a result of insufficient cutting or as a result of short-circuits.
The corresponding fuse address can already be indicated, in one embodiment of the invention, by a marking disposed on the printed circuit board, for example by a number denoting the fuse address. As a result, the assembly of the releasing device is simplified and interchange of various fuse addresses can be avoided.
Furthermore, it is advantageous if the conductor tracks on the printed circuit board have a meander-shaped course. This makes it possible to filter out high-frequency radiations and thereby to avoid their effect on the integrated circuit.
The invention is explained in greater detail by reference to exemplifying embodiments.